1. Field of the Invention
The invention relates generally to low power voltage references and, more particularly, to low power reference drivers formed on an integrated circuit (IC) chip.
2. Description of the Prior Art
A regulated voltage source is required in many electronic systems. In systems fabricated on a semiconductor IC chip, the voltage reference has generally been implemented off the chip. On-chip voltage references have recently been developed and are described, for example, in an article by Tsividis et al., entitled "A CMOS Voltage Reference," IEEE J. Solid State Circuits, V. SC-13, No. 6, Dec. 1978, pp. 774-778, and an article by Blaushild entitled "A New NMOS, Temperature Stable Voltage Reference," IEEE J. Solid State Circuits, V. SC-13, No. 6, December 1978, pp. 767-773. However, neither of the voltage references described in these articles are characterized by low output impedance at low power.
The reference Tsividis et al., at page 774, described several advantages of a CMOS voltage reference. Among these advantages are that CMOS design places bipolar devices at the disposal of a circuit designer and, when operated in the subthreshold region, provides a temperature insensitive reference.
Recently, CMOS dynamic RAM ICs have been developed to reduce power consumption. It is of critical importance that the voltage reference utilized in these systems dissipates very low power so that the overall low power consumption of CMOS DRAM is not significantly degraded.
These IC memory circuit arrays, and many other IC systems, require a voltage reference driver capable of supplying a high level of current without changing the reference voltage. For example, in an IC memory array, this current is required to charge the bit lines and storage capacitors in the memory array to the required reference voltage. To achieve the characteristics of a good driver, the voltage reference must have a low output impedance.
The output impedance of the voltage reference and the load resistor form a resistive voltage divider circuit. If the driver is supplying current to the load then the output voltage from the driver will be decreased by an amount equal to the current multipled by the output impedance. Thus, a low output impedance is required to provide a stable voltage reference and to supply high current.
Additionally, a low output impedance voltage reference driver also provides for a low RC charging time where R is the output impedance of the voltage reference and C is the capacitance of the IC circuit. This low charging time is of critical importance to implementing high speed memory arrays and other IC high speed circuits.
Accordingly, a great need exists in the IC device industry for a low power, low output impedance, on-chip voltage reference.